Planar display lamp and method of forming a light scatterer pattern

ABSTRACT

A plane display lamp using one or two dot-like light sources. This plane display lamp comprises a plate-like light guiding member; a bottom plate covering a bottom surface of said light guiding member; a casing frame covering side faces of said light guiding member; a diffusing sheet covering a top surface of said light guiding member; and dot-like light sources provided on one side face or on two side faces opposite to each other of said light guiding member and emitting light to said light guiding member, and a light scatterer pattern is provided on a bottom surface of the light guiding member. When a side face thereof is inclined, a light scatterer pattern may be provided also on the inclined side face or just below the inclined side face.

TECHNICAL FIELD

The present invention relates to a planar display lamp. Morespecifically this invention relates to a planar display lamp based on alight guiding system in which a bottom surface of light guiding memberhas a light scattering function for homogeneously emitting light to theoutside, and further to a method of forming a light scatterer patternrealizing a light scattering function.

BACKGROUND ART

A planar display lamp (with the display area of several tens cm² orless) is used in various types of devices and equipment used indoors todisplay a state of or an instruction for an operation of the devices orequipment. One example of the planar display lamp is a pilot lamp inwhich a light source such as a compact incandescent lamp or alight-emitting diode (LED) is attached to a casing having a coloredplastic plate surface. In these types of lamps, when a letter or a signis to be displayed on a display surface, as the luminance just above thelight source is higher than that in the peripheral area of the displaysurface, non-uniformity in luminance on the display surface is large,and the letter or sign displayed on the surface can not well be visuallyrecognized. Further these types of display lamps allows onlydiscrimination between two stages basically by turning ON or OFF thelamp. Also there is a planar display lamp in which a light sourcecapable of emitting light changing its color is provided under asemitransparent plastic plate, but non-uniformity in luminance variesaccording to a color of emitted light more remarkably as compared to thecase of single color planar display lamp, so that the adaptability to bevisually recognized is further lower.

As a means for reducing non-uniformity in luminance, there has beenknown the method used in a planar illumination device applied as a backlight for a liquid crystal display unit. In this method, a plate-likelight guiding member is used and a linear light source such as afluorescent light source or a plurality of dot-like light sources suchas LEDs are provided around the plate-like light guiding member therebyimplementing a planar light source. Generally a reflection layer withdistributed reflectivity is provided on a bottom surface of the lightguiding member so that the light sources emit light with substantiallyhomogeneous intensity from a surface of the plate-like light guidingmember.

In the pilot lamp with the conventional type of light source such as anincandescent lamp or an LED attached therein as described above,non-uniformity in luminance is large on the light-emitting surface, sothat the visibility of displayed contents is low and also the displayquality is disadvantageously low.

Further with the plane display lamp having a light source capable ofemitting light changing its color to provide light with a desired color,it is impossible to obtain the excellent display quality.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a plane display lamp withreduced non-uniformity in luminance by using a plate-like light guidingmember.

It is another object of the invention to provide a plane display lampwith reduced power consumption and having a light source which caneasily be driven.

It is still another object of the invention to provide a plane displaylamp having two dot-like light sources.

It is another object of the present invention to provide a plane displaylamp having only one dot-like light source, yet capable of reducingnon-uniformity in luminance on a light-emitting surface.

It is another object to provide a method of forming a light scattererpattern printed on a bottom surface of a plate-like light guidingmember.

In a first aspect of the present invention, one dot-like light source isprovided at a center of each of the opposite side faces of a rectangularplane light guiding member respectively. To reduce non-uniformity inluminance of light coming out from a surface of this light guidingmember, a light scatterer pattern with reflected light intensitytwo-dimensionally distributed thereon is formed on a bottom surface ofthe light guiding member.

As the dot-like light source, one LED chip loaded on the same package ora plurality of LED chips, for instance, for three RGB elementary colorsloaded adjacent to each other on the same package may be used. In thelatter case, as a plurality of LEDs are provided adjacent to each other,when light for each color is emitted, non-uniformity in luminance doesnot substantially change, so that a plurality of states can be displayedby using lights for different colors.

What is important in the present invention is a light scatterer patternformed on a rear side of a light-emitting surface of a light guidingmember so that light emitted from a dot-like light source is taken by aplate-like light guiding member to give uniform brightness, namelyuniform luminance on the light-emitting surface of the light guidingmember. By giving a certain level of regularity to a pattern form, ithas become possible to provide homogeneous luminance distribution on anentire light-emitting surface of a light guiding member and also toprovide planar displays having apparently uniform brightness.

To realize the optimal pattern as described above, how to form a dotpattern of a light scatterer on a bottom surface of the light guidingmember is important.

A light scatterer dot pattern formation method according to a secondaspect of the present invention comprises the steps of:

a) forming a light scatterer homogeneously all over a bottom surface ofa light guiding member for assessment having the same size and made fromthe same materials as said light guiding member;

b) assembling said plane display lamp;

c) measuring luminance at each coordinate point on a light-emittingsurface of said plane display lamp;

d) converting the measured luminance at each coordinate point throughinverse-proportional operation to standardized value using the lowestvalue in a distribution the luminance as a reference;

e) calculating an area of a light scatterer dot at each coordinate pointfrom the standardized value obtained from the conversion in the previousstep; and

f) forming a pattern of light scatterer dots each area thereof iscalculated in the previous step on a bottom surface of a light guidingmember different from that for assessment.

A third aspect of the present invention provides a plane display lampwhich can reduce non-uniformity in luminance on the light-emittingsurface even when only one dot-like light source is used. In the planedisplay lamp using one dot-like light source according to the presentinvention, three of the four side faces of the rectangular planar lightguiding member are inclined side faces. On a central one of these threeincluded side faces, or on a bottom surface of the light guiding memberjust below the side face, one dot-like light source is provided. Furtherprovided on a bottom surface of the light guiding member just below thetop surface of the light guiding member is a light scatterer dot patternformed according to the method according to the second aspect of thepresent invention as described above, and further a light scattererpattern is provided on a bottom surface of the light guiding member justbelow an inclined side face adjacent to an area where light from thedot-like light source does not fully reach and the luminance isinsufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a exploded perspective view showing one example of a planedisplay lamp according to the present invention;

FIG. 2 is a view showing a light-emitting surface with a X-Y coordinatesystem divided to four fields;

FIG. 3A and FIG. 3B are views each showing a table of measured luminancedistribution on a plane display lamp in a case where high reflection inkis printed all over a bottom surface of a light guiding memberrespectively;

FIG. 4 is a view showing the luminance distribution in FIG. 3 with thecontour lines;

FIG. 5A and FIG. 5B are views each showing a table of standardized valuedistribution respectively;

FIG. 6A and FIG. 6B are views each showing a table of calculatedcircular dot radiuses;

FIG. 7 is a view showing a printed circular dot pattern;

FIG. 8 is a view showing a table of measured luminance distribution on aplane display lamp in a case where a circular dot pattern is printed ona bottom surface of the light guiding member;

FIG. 9 is a exploded perspective view showing another example of theplane display lamp according to the present invention;

FIG. 10 is a view showing with contour lines the luminance distributionwhen there is provided one dot-like light source on a bottom surface ofthe light guiding member;

FIG. 11 is a perspective view showing a light guiding member accordingto the present invention;

FIGS. 12A, 12B, 12C and 12D are views showing a top surface and a sidesurface of the light guiding member shown in FIG. 11;

FIG. 13 is a view showing an example in which an LED is provided on abottom surface of a light guiding member;

FIG. 14 is a view showing another example in which an LED is provided ona bottom surface of the light guiding member; and

FIG. 15 is a view showing an example in which a dot-like light source isprovided inside the light guiding member.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A exploded perspective view of a plane display lamp according to a firstembodiment of the present invention is shown in FIG. 1.

This plane display lamp 10 has a light guiding member 12 comprising arectangular transparent acrylic resin plate with the size of 50 mm×25mm×5 mm. In this embodiment, each side face of the light guiding memberis vertical to the top surface as well as to the bottom surface thereof.

In this light guiding member 12, dot-like light sources 14 a, 14 b areprovided at central positions of side faces in the opposite shorter edgesides respectively. An LED with the output of 1.5 mW for a forwarddirection current of 20 mA and with the main wavelength of green colorlight of 530 nm from Nichia Kagaku Kogyo (K.K) is used as the dot-likelight source. The size of one LED (semiconductor chip) is 0.3 mm×0.3 mm,and the size of an aperture (light-emitting section) as a light outletport of the LED package with one chip loaded therein is about 1 mm×2 mm.

This transparent acrylic light guiding member 12 has a white bottomplate 16, four side faces of which are covered with a white casing frame18. A diffusing sheet 20 is adhered on a top surface of, namely in thelight-emitting surface side of the white casing frame 18. White ABSresin is used for the white casing 18 as well as for the white bottomplate 16.

Further a light scatterer having a predetermined pattern was formed withthe highly reflective white ink from Teikoku Ink Seizou (K.K) on abottom surface 13 of the light guiding member 12. The pattern of thelight scatterer is generally a circular dot.

Although a color of the casing 18 and bottom plate 16 is typicallywhite, other colors such as silver may be used. In the case of singlecolor light source, any appropriate color may be selected according tothe wavelength of the light.

A specific sequence of designing a printed pattern is described indetail below. At first the light guiding member 12 with the highlyreflective white ink printed on the entire bottom surface thereof isprepared, this light guiding member 12 is placed in the white casing 18and covered with the white bottom plate 16 with a diffusing sheetadhered on a light-emitting surface of the white casing, and then aplane display lamp for designing a light scatterer pattern is assembled.Then the luminance distributed on the light-emitting surface when the 20mA current is flown through each LED is measured.

As the LEDs 14 a, 14 b are provided at central positions of the sidefaces 15 a, 15 b in the side of opposite shorter edges of the lightguiding member 12 respectively as described above, when thelight-emitting surface is divided with two lines perpendicular to eachother into four equal regions, the luminance distribution on each regionis identical, so that it is necessary only to measure the luminancedistribution on one of the four regions. FIG. 2 shows a state where thelight-emitting surface is shown with an X-Y coordinate system. Thecoordinate plane is plotted with a corner of the light-emitting surfaceas the origin and the X-axis was divided to 25 equal zones and also theY-axis to 50 equal zones. This figure shows the state where thelight-emitting surface was divided with the two lines 22, 24 crossingeach other at right angles at a center of the light-emitting surface tofour regions. The luminance distribution is measured on the quadrantregion 26 shadowed with inclined lines.

When the luminance distribution on the region 26 is measured, theluminance distribution on the entire light-emitting surface can beobtained by applying the measured luminance distribution to the otherregions symmetrically in the horizontal direction as well as in thevertical direction against the two lines 22, 24 perpendicular to eachother respectively.

The measured luminance distribution for the region 26 was shown in FIG.3A and in FIG. 3B. FIG. 3A and FIG. 3B show tables each showingdistribution of luminance (cd/m²) at each point (x, y) from the originto the coordinate point 12 in the X-axial direction and from the originto the coordinate point 25 in the Y-axial direction. The tables showthat the luminance is lowest at the coordinate point (0, 0) and becomeshigher in the coordinate area close to the LED. Non-uniformity inluminance in this case is 4.4 times when expressed by themaximum/minimum ratio on the plane.

FIG. 4 shows the luminance distribution on the entire light-emittingsurface based on the tables of the measured luminance distribution forthe region 26 with contour lines 28. From the contour lines indicatingthe luminance distribution, it can be understood that the emitted lightfrom the LED extends in the radial form and the extension angle 2θ isabout 60 degrees.

FIG. 5A and FIG. 5B show tables each showing the standardized luminancedistribution obtained by standardizing the distribution of measuredluminance through inverse-proportional conversion using the minimumvalue in the distribution of luminance shown in FIG. 3A and FIG. 3B as areference. The minimum value in the distribution of luminance shown inFIG. 3A and FIG. 3B is 98.76 cd/cm² at the coordinate point (0, 0), andluminance values at other coordinate points are standardized throughinverse-proportional conversion. Namely a standardized value at eachcoordinate point is calculated (standardized) through the followingequation:

Standardized value=A×98.76/measured luminance

wherein A indicates a proportional constant. The obtained standardizedvalue is in inverse proportion to the luminance, and as the luminance ishigher, the standardized value is lower. The standardized values shownin FIG. 5A and FIG. 5B are those when A is equal to 1.

The method of allocating a circular dot of a light scatterer to eachcoordinate point is described below. FIG. 6A and FIG. 6B are tables eachshowing the radiuses of circular dots per unit area (mm²) calculatedfrom the standardized values shown in FIG. 5A and FIG. 5B through theequation of standardized value=A×π×(radius)² assuming that A is equal to1 (A=1). Each numerical value in these tables indicates the diameter ofa circular dot at each coordinate point, and a plate for a print patternis prepared assuming that the diameter of a circular dot is that of aprinted circular dot in a square segment with the area of 1 mm².

A pattern of circular dots is printed on a bottom surface of the lightguiding member using the prepared plate for the print pattern. FIG. 7shows one example of a printed circular dot pattern 30. A solid circle32 in this figure shows a circular dot, and the reflectivity in thecircular dot section is high. The light scatterer pattern formed with apattern of the circular dots as described above has the feature that thereflectivity is minimum at the sections “a” and “b” on the surface.

A plane display lamp is assembled using the light guiding member 12 withthe circular dot pattern 30 printed on the bottom surface thereof.Namely the white bottom plate 16 is adhered to a bottom of the lightguiding member 12, the white casing frame 18 is set therein, and thediffusing sheet 20 is adhered to the light-emitting surface. In theplane display lamp as described above, the LEDs 14 a and 14 b are turnedON, and the luminance distribution is measured. The measured values areshown in FIG. 8. At the coordinate point (22, 10), the maximum luminancewas 118.9 cd/m², while the minimum luminance at the coordinate point (4,12) was 60 cd/m², and non-uniformity in luminance in terms ofmaximum/minimum ratio is 1.98 times, which indicates that thenon-uniformity is suppressed to a level lower than 2 times.

To obtain more uniform luminance distribution, the method is alsoeffective in which the luminance is once corrected by the patterndesigning method described above, further the luminance distribution ismeasured in the same way, distribution of standardized values isobtained, and the luminance distribution obtained first is subjected tosecondary correction. By repeating correction a required number of times(n), homogenous and high luminance can be obtained on the light-emittingsurface of the light guiding member.

An example of a single color light source in which one LED chip ispackaged in one dot-like light source has been described above, and inthe case where a plurality of LED chips are provided in on LED package,regardless of which of the plurality of LED chips emits light, as ageometrical and positional relation between the light guiding member andthe LED chip is kept substantially constant, so that the light emittedfrom the LED chip is homogeneously distributed from the light-emittingsurface of the light guiding member. Namely a light-emitting surfacewith the generally homogeneous luminance distribution is obtained. Forinstance, LED chips for emitting lights with red (R), green (G), andblue (B) colors are packaged in the same LED package so that a distancebetween the two adjoining chips is about 1 mm, and the package is usedas a light source. This display lamp can be turned ON switching betweenthe R, G and B colors, and further LED chips for two or three colors cansimultaneously be turned ON to emit light with a mixed color. As thedistance between LED chips is small as described above, change ofnon-uniformity in the luminance at each light-emitting point for thesame dot pattern can visually be recognized little. The plurality of LEDchips described above may emit light having the same color. In thiscase, the displays in which the luminance level may be changed isimplemented.

In the embodiment described above, a longer edge of the rectangular flatlight guiding member is 50 mm, but the length is allowable in the rangefrom about 20 to about 200 mm. The luminance largely depends onintensity of light emitted from an LED, and when the light has theintensity similar to that described in the example described above, theluminance of the displays becomes lower as the size becomes larger.Further it is necessary to redesign the dot pattern each time the sizeof the light guiding member is changed.

Further in the embodiment described above, the light scatter was formedwith circular dots, but a form of the dot is not limited to a circularone. Rather a square pattern which has the same form as the squaresegment is better because higher consistency between the luminance andthe area ratio can be realized. Further a form of light scattererpattern may be changed to many other ones including a rhombic one.

Further, the screen printing method was used as a method of forming alight scatterer in the embodiment described above, but it is possible toform a light scatterer pattern by applying various types of organic orinorganic light scattering materials (mainly white paint) onto a bottomsurface of a light guiding member by such a method as the offsetprinting or ink-jet printing.

Instead of applying a highly reflective material as described above, thelight may be reflected by roughing a bottom surface of the light guidingmember. The methods which can be used make rougher bottom surface of alight guiding member include mechanically roughing the bottom surface,forming a number of fine irregularities, for instance, by the sandblastmethod, directly performing processing for generation of irregularitiesto a metal mold for injection molding and transferring theirregularities to a bottom surface of the light guiding member of SCmachining. Basically these methods are based on utilization of the lightscattering and reflection effect provided by roughing the bottomsurface.

Second Embodiment

FIG. 9 shows a plane display lamp according to a second embodiment ofthe present invention. This display lamp 22 has the configuration inwhich, in the structure shown in FIG. 1, a letter or a sign 34 isprinted on the diffusing sheet 20, or a light shielding plate 36 madefrom a metal or plastics is adhered on the diffusing sheet 20. Also theconfiguration is allowable in which an opaque letter or a sign isprinted or adhered on a glass or transparent glass or plastic sheet.With the configurations as described above, it is possible to obtain aplane display lamp capable of displaying a letter or a sign.

Third Embodiment

In the first and second embodiments of the present invention, twodot-like light sources, namely two LEDs are provided at a centralposition of each of the side faces in the side of the shorter edges ofthe light guiding member opposing to each other respectively. However,realizing a plane display lamp insuring high uniformity in luminanceonly with one dot-like light source provides a number of advantagesincluding cost reduction, easiness of the manufacture, reduced powerconsumption, and the like.

In the first embodiment, when the LED 14 b is removed, the luminancedistribution on the light-emitting surface corresponding to that shownin FIG. 3 is as shown in FIG. 10. In FIG. 10, the regions separated fromeach other with contour lines 38 are indicated by the signs 38-1, 38-2,38-3, 38-4, 38-5, and 38-6. As only one piece of LED is provided, lightfrom the LED does not fully reach corners of the light-emitting surfacein the side of the LED 14, so that the luminance in the region 38-6 isinsufficient. This phenomenon occurs because intensity of the lightemitted from the LED is higher at positions closer to the center of thelight-emitting section as well as to the normal line thereto and lowerat positions farther from the center (in the direction at 90 degreesagainst the normal line and does not directly reach corners of the lightguiding member in the LED side. The luminance in the highest luminanceregion was 7 times or more higher as compared to that in the lowestluminance region where the light from the LED does not fully reach.

In the plane display lamp with only one LED provided therein, a dotpattern is printed on a bottom surface of the light guiding member bythe circular dot pattern formation method similar to that employed inthe first embodiment. In this case, even when white paint is applied tothe entire bottom surface of the light guiding member in theinsufficient luminance region 38-6 and at the same time 0.09 mm² dot isprovided per 1 mm² (area ratio is 11) in the highest luminance region18-1, the luminance in the highest luminance region 28-1 is 2 times ormore higher as compared to that in the insufficient luminance region28-6, so that it is difficult to obtain a light-emitting surfaceinsuring uniform light emission.

To solve the problem described above, the present inventors investigatesthe possibility of development of a means capable of reducingnon-uniformity in the luminance on a light-emitting surface of a lightguiding member even in a plane display lamp with only one LED providedtherein. At first, the state of light in a light guiding member isdiscussed in detail below. The light coming into a light scattererpattern printed on a bottom surface of the light guiding member isscattered by this light scatterer pattern in the light guiding member.On the other hand, the light introduced to a region where a lightscatterer pattern is not present follows the Snell's law, and is totallyreflected on a surface of the light guiding member, or is emitted to aspace outside the light guiding member. Namely assuming that an anglebetween a normal to a surface of a light guiding member and a light beaminside the light guiding member is ψ and a refraction index of the lightguiding member is n, the light beam follows the Snell's law, and istotally reflected on a surface of the light guiding member when n·sinψis larger than 1. So long as this condition is satisfied, the light beamis repeatedly reflected inside the light guiding member, and does not goout of the light guiding member. When n·sinψ is smaller than 1, thelight beam is emitted from the light guiding member. In the case of aplane display lamp, as each face excluding the light-emitting surface iscovered with a white casing, the light emitted from the light guidingmember is partially reflected by the white casing and goes back into thelight guiding member.

As described above, behaviors of light in a light guiding memberincluding a casing are very complicated, but a percentage of the lightscattered by the light scatterer and emitted therefrom is substantiallyhigh. Therefore, it has been found that, by appropriately selecting asection where the light scatterer is to be formed, it is possible toprovide uniform luminance distribution on a light-emitting surface.

Based on this recognition, the inventors have provided a light scattereron each side face of a rectangular light guiding member. It can beexpected that, by providing a light scatterer on a side face of thelight guiding member close to the insufficient luminance region 38-6,the light otherwise emitted from the side face to the outside caneffectively be utilized. When actually a printed pattern is provided onall over the necessary side face, the luminance in the insufficientluminance region remarkably increased.

Printing light scatterer patterns on both a bottom surface and sidefaces of a light guiding member required a very complicatedmanufacturing process. So the present inventors have devised the methodin which a printed pattern is formed only on a bottom surface of a lightguiding member and is not required to be formed on side faces thereon.

This method is described below with reference to the third embodiment.FIG. 11 and FIGS. 12A, 12B, 12C and 12D shows a light guiding member 40according to this embodiment. FIGS. 12A, 12B, 12C and 12D are viewsshowing a top surface and side surfaces of the light guiding member 40according to this embodiment.

The light guiding member 40 has a plate-like form as shown in FIG. 11,and comprises a bottom surface 44 opposite to the top surface, and sidefaces 50, 52, 54, and 56. The three side faces 50, 52, 54 excluding theside face 56 are inclined. Namely the side faces are inclined so thatthe distance between two opposing side faces becomes larger as it goesfarther from the top surface 42 and closer to the bottom surface 44. Theinclination of each of the three side face in this embodiment is, forinstance, 45 degrees.

Provided on the inclined side face 50 is a recessed section 58 extendingfrom a top surface of the light guiding member 40 to a bottom surfacethereof at a center of the inclined side face. The recessed section 58should preferably have a form allowing installation of the LED 14 sothat the light emitted from the LED 14 and advancing straight over theshortest distance will be introduced onto the opposite side face 56 atsubstantially right angles.

As described above, when there is provided only one LED, there is theregion 38-6 where the luminance 38-6 is insufficient (Refer to FIGS.12A, 12B, 12C and 12D). To overcome the problem, highly reflective inkis printed over the entire bottom surface of the light guiding member 40with one LED provided therein as shown in FIG. 11 is prepared, and aplane display lamp for designing a light scattering pattern is assembledusing this light guiding member to design a circular dot pattern. Thecircular dot pattern designed as described above is printed on a bottomsurface of the light guiding member just below a top surface thereof. Inaddition, a pattern 62 is printed all over in part on bottom surfacesjust below the inclined side faces 50, 52, 54 and close to theinsufficient luminance region 38-6 respectively. With the printedpatterns 62, the luminance in the insufficient luminance region 38-6 isincreases to a level equal to or higher than that in the region 38-5,and the plane display lamp insures uniformity in the luminance with thelight from one LED 12.

As a variant of the light guiding member as described above, thefollowing one is conceivable. In the light guiding member 40 shown inFIG. 11, the same effect can be achieved, for instance, by printing apattern on the entire not-inclined side face 56. Further it is alsopossible to transfer a light-scattering pattern by means of a metal moldonto side faces of the light guiding member in place of printing thepattern on each side face thereof.

Further it is also possible to deform a light guiding member, forinstance, by inclining only a side face on which an LED is mounted, orby also inclining a side face with no LED mounted thereon and oppositeto the side face with an LED mounted thereon. In addition, a side faceof the light guiding member may be inclined not over the full lengthfrom the top surface to the bottom surface, but for instance from thetop surface to the middle of each side face.

Fourth Embodiment

Next a fourth embodiment of the present invention is described withreference to FIG. 13. This embodiment is a variant of the embodimentdescribed with reference to FIG. 11 and FIGS. 12A, 12B, 12C and 12D, andin this embodiment, the LED 14 is provided on a bottom surface of thelight guiding member just below the inclined side face of the lightguiding member 40. The light emitted from the LED 14 advances goes intothe light guiding member from its bottom surface and is reflected andscattered by the inclined side face 50 or a casing (not shown) and isled to inside of the light guiding member 40.

Further to raise the efficiency in reflection and scattering, a recessedsection 70 having a curved surface for reflecting or scattering light isprovided on the inclined surface 50 just above the LED. The luminancedistribution on the light-emitting surface of the plane display lampcould be uniformed by making a form of the surface of this recessedsection 70 aspheric.

Fifth Embodiment

A fifth embodiment of the present invention is described with referenceto FIG. 15. This embodiment is a variant of the embodiment of thepresent invention shown in FIG. 11, and in this embodiment, a hole forengagement is provided inside the light guiding member 40 adjacent tothe inclined side face 50, and a dome-shaped resin-shielded type of LED72 is provided in the hole 40. The light emitted from the resin-shieldedtype of LED 72 is reflected and scattered by the inclined side face 50or a casing (not shown) and is led to inside of the light guiding member40.

Inclining one or a plurality of side faces of a light guiding memberlike in the third to fifth embodiments provides advantages also in themanufacture of a light guiding member. A light guiding member isgenerally manufactured by molding a transparent resin such as acrylicresin into a desired form with a metal mold. When one or a plurality ofside faces of the metal model are inclined, the light guiding member mayeasily be released from the metal mold without damaging the side facesof the light guiding member.

In the third to fifth embodiments of the present invention, only thelight guiding member is shown, and a casing covering the light guidingmember is not shown. This casing functions also to reflect light emittedfrom the light guiding member, so that the color is typically white likein the first embodiment, but the color may be other one like, forinstance, silver. In the case of a single color light source, anappropriate color can be selected according to the wavelength of thelight emitted from the light source.

Industrial Applicability

With the present invention, as an LED, which is a semiconductor chip, isused as a light source, a high voltage circular as a drive circular isnot necessary, and also a plane display lamp with long lifetime and highreliability can be realized. Further as one or two compact size LEDs maybe used therein, a small size, light weight, and compact plane displaylamp with low power consumption can be obtained. When two LEDs are usedin the plane display lamp as described above, a light guiding memberwith a light scattering dot pattern formed thereon by the patternformation method according to the present invention is used, so that theuniform luminance distribution can be obtained. Further when a lightguiding member with inclined side face(s) is used, alight scatteringpattern is provided on the side faces adjacent to the insufficientluminance region or on a bottom surface of the light guiding member justbelow the side faces, so that the uniform luminance distribution can beobtained.

What is claimed is:
 1. A method of forming a light scatterer dot patternon a bottom surface of a plate-like light guiding member in a planardisplay lamp including said light guiding member; and bottom platecovering a bottom surface of said light guiding member; a casing framecovering side faces of said light guiding member; a diffusing sheetcovering a top surface of said light guiding member; and dot-like lightsources provided on one side face or on two side faces opposite to eachother of said light guiding member and emitting light to said lightguiding member; said method comprising the steps of: a) forming a lightscatterer homogeneously all over a bottom surface of a trial lightguiding member, the trial light guiding member having a size andcomposition that is substantially equivalent to said light guidingmember; b) assembling a trial planar display lamp using said trial lightguiding member prepared in step a; c) measuring a luminance value ateach coordinate point on a light-emitting surface of said trial planardisplay lamp; d) converting the measure luminance value at eachcoordinate point to standardized value by applying aninverse-proportional operation to the measured luminance value, using alowest value in a distribution of the measured luminance values as areference value; e) calculating an area of a light scatterer dot at eachcoordinate point from the standardized value obtained from theconversion in step d; and f) forming a pattern of light scatterer dotseach area thereof is calculated in step e on a bottom surface of a lightguiding member different from said trial light guiding member.
 2. Themethod according to claim 1 further comprising the steps of: g)assembling a second trial planar display lamp using the trial lightguiding member prepared in step f; h) measuring a further luminancevalue at each coordinate point on a light-emitting surface of the secondtrial planar display lamp; i) converting the further measured luminancevalue at each coordinate point to standardized value by applying aninverse-proportional operation to the further measured luminance value,using a lowest value in a distribution of the further measured luminancevalues as a reference value; j) calculating an area of a light scattererdot at each coordinate point from the standardized value obtained fromthe conversion in step i; k) forming a pattern of light scatterer dotseach area thereof is calculated in step j on a bottom surface of a lightguiding member different from the light guiding member prepared in stepf; and l) repeating the operating sequence from step g to step k n times(n being an integer larger than 0) to the light guiding member preparedin step k.
 3. The method according to claim 1, wherein the conversion tothe standardized value in step d is performed using the followingequation: Standardized value=Lowest luminance value/measured luminanceat each coordinate point.
 4. The method according to claim 2, whereinconversion to the standardized value in the steps d and i is performedthrough the following equation: Standardized value=Lowest luminancevalue/measured luminance at each coordinate point.
 5. The methodaccording to claim 3 or 4, wherein said light scatterer dot has a formsatisfying the following condition: Standardized value=A×dot areawherein A indicates a proportional constant.
 6. The method according toclaim 3 or 4, wherein, when said light scatterer dot is a circular dot,the radius thereof is calculated through the following equation:Standardized value=A×π×(radius)² wherein A indicates a proportionalconstant.
 7. The method according to any of claim 1 or 2, wherein saidlight scatterer dot pattern is formed so that a reflection factor isminimum at a position adjacent to each of said dot-like light sources.8. A planar display lamp comprising: a plate-like light guiding member,a bottom surface thereof having a light scattering means; a bottom platecovering a bottom surface of said light guiding member; a casing framecovering side faces of said light guiding member; a diffusing sheetcovering a top surface of said light guiding member; and dot-like lightsources provided on one side face or on two side faces opposite to eachother of said light guiding member and emitting light to said lightguiding member; wherein said light scatterings a light scatterer dotpattern formed by the method according to claim 1 or 2 on a bottomsurface of said light guiding member just below a top surface thereof.9. A planar display lamp comprising: a plate-like light guiding memberhaving a rectangular top surface, a rectangular bottom surface, and fourside faces each vertical to said top surface as well as to said bottomsurface, a bottom surface of said light guiding member having a lightscattering means; a bottom plate covering a bottom surface of said lightguiding member; a casing frame covering side faces of said light guidingmember; a diffusing sheet covering a top surface of said light guidingmember; and dot-like light sources provided on one side face or on twoside faces opposite to each other of said light guiding member andemitting light to said light guiding member; wherein said lightscattering means is a light scatterer dot pattern formed by the methodaccording to claim 1 or 2 on a bottom surface of said light guidingmember just below a top surface thereof.
 10. A planar display lampcomprising: a plate-like light guiding member having a rectangular topsurface, a rectangular bottom surface, and four side faces, at least oneof which has an inclination extending from said top surface toward saidbottom surface, a bottom surface of said light guiding member having alight scattering means; a bottom plate cove ring a bottom surface ofsaid light guiding member; a casing frame covering four side faces ofsaid light guiding member; a diffusing sheet covering a top surface ofsaid light guiding member; and one dot-like light source emitting lightto said light guiding member; wherein said light scattering means is alight scatterer dot pattern formed by the method according to claim 1 or2 on a bottom surface of said light guiding member just below a topsurface thereof.
 11. The planar display lamp according to claim 8:wherein said light scatterer dot pattern is formed so that a reflectionfactor is minimum at a position adjacent to each of said dot-like lightsources.
 12. The planar display lamp according to claim 9: wherein saidlight scatterer dot pattern is formed so that a reflection factor isminimum at a position adjacent to each of said dot-like light sources.13. The planar display lamp according to claim 10: wherein said lightscatterer dot pattern is formed so that a reflection factor is minimumat a position adjacent to each of said dot-like light sources.